A variety of electronic device systems each including multiple electronic devices serving as units have been available. One known example is an electronic device system including multiple electronic devices that are arranged side by side in a predetermined direction and assembled together to achieve electrical connection between them. A typical example of this electronic device system is a remote terminal device for a PLC.
A remote terminal device includes a single communication unit and one or more input-output (I/O) units, which are communicable with the communication unit through corresponding serial bus lines and unidirectional communication lines. The communication unit and the I/O units are typically designed as building blocks that are to be joined together.
The remote terminal device with the above structure is described in detail in, for example, Japanese Unexamined Patent Application Publication No. 2016-129179 (Patent Literature 1).